blackbeauty

Hi everyone,

I've been having a hell of a time trying to get a 1989 305 TPI with factory tune running right (not the one mentioned in my signature), and I need your help...

When the engine is stone cold I turn the key and it starts and appears to run normally. Even when the engine becomes warm it still smells a little rich. I would expect by this point for that to have subsided once it's entered closed loop. While the car will rev there is a faint shudder. An untrained person may not notice it but I do.

If I shutdown the engine and try to start it back up straight away it has a hell of time trying to start. If I keep cranking long enough it will eventually start, but sometimes it won't. If I wait 10 seconds before starting the car again, the fuel pump will prime as expected and I can typically start the engine, sometimes with a little extended cranking.

Also, if the engine is stone cold and I turn the key to the run position, let the fuel pump prime, wait a couple of minutes, then turn the key further the engine will turn over but not start. Turn the key off fully, wait 10 seconds, turn the key, fuel pump primes and the engine will struggle a little but typically starts. There's a fuel vapour smell too. Plugs are fouling up with black deposits.

I do not have a fuel pressure gauge to check with, but I suspect that fuel is leaking somewhere because I can smell it when I prime the fuel lines after the engine has been sitting over night. Also the fact that I can't start it after having primed the fuel lines for a couple of minutes. Surely the pressure is dropping off and fuel is going somewhere?

I have checked the resistance of the factory Multech 19lb injectors and all are 17ohms when cold. After running the engine for a few minutes I shutdown the engine and checked them again. They still all read 17ohms.

I have also replaced the oil pressure switch with a new one.

I have data logged the ALDL and I don't see anything wrong. The MAT and coolant temperature sensors both give sensible readings and close enough match the other 1989 Trans Am I have which sits in the garage along side it, when both engines are stone cold.

As I said, I don't have a fuel pressure gauge. So I pulled apart the upper plenum and removed the fuel rail from the intake manifold. I noticed it was wet at the top of the tubes at the back right hand side of the engine. I reconnected the minimum necessary and turned the key to prime the fuel lines. I was expecting to see at least an injector leaking but nothing, nothing at all.

I figured it therefore must be the fuel pressure regulator, so I took that apart. But no, the diaphragm looks fine as far as I can see. I don't notice any holes/rips anywhere.

Before I took the engine apart, I tested a known good ECM with this engine and it made no difference.

So this is where I'm at and I'm stumped. I would appreciate some help!

Thanks,

86T/A_Ram_Air

Sounds like the injectors are leaking down. the multec injectors are crappy. especially if they sit

blackbeauty

Thanks for your reply after reading my long post!

I'd certainly thought that myself, since they have a bad reputation. But wouldn't they leak when I did the test with the fuel rail out of the intake manifold and then primed the fuel system?

86T/A_Ram_Air

in theory yes. but not necessarily. you could have the issue of them not "closing" all the way after the initial spray or leaking down when they are warm. what I would do is check your fuel pressure cold, cold while running and then hot running and hot off and watch for a deviation in pressure

A fuel pressure gauge is a good tool to own especially when working on fuel injected cars. you can get a decent one for a good price or you might be able to rent one from a parts store but it all starts with fuel pressure

blackbeauty

That sounds like a good idea, thanks.

I tried many places to get a fuel pressure gauge but no one has one, which isn't too surprising in my part of the world. Could only buy an expensive kit which had adapters for lots of other cars. So I've ordered one from Summit so I imagine it'll turn up in the new year.

I primed the fuel line a few times over this evening and noticed a couple of injectors did produce one or two drops from them. I imagine this isn't normal at all and is a sign of something more sinister?

If so, I get the feeling it will be wise simply to go and buy replacement injectors and install them.

86T/A_Ram_Air

I would make sure but I do really think the injectors are suspect at best. I would use South bay for injectors. they sponsor this site and have a very good reputation

rgarcia63

My 2 cents. If these injectors are indeed original equipment, don't you think it time to toss them? Even if they're not leaking, I don't think they're flowing/spraying properly by the symptoms you gave.
I know you don't want to just throw money at it, but it would make things easier to diagnose with properly working injectors.
When I bought my 88' in 96' that was the first thing I did and deleted the cold start by using a 89' bin. That solved 80% of the driveability issues I had.

blackbeauty

Thanks very much for your thoughts guys. I've bought a set from Southbay so am really looking forward to receiving those and installing them.

This is someone else's car I'm fixing so wanted to be certain it was the injectors since I'm effectively spending their money. If it were mine I'd replace them in a heart beat.

86T/A_Ram_Air

Good deal. Let us know how you make out

blackbeauty

Well guys I don't know if I'm any further ahead. I have installed some fuel injectors from SouthBay, put in another fuel pressure regulator diaphragm and the car behaves exactly as it did before.

Before starting the engine for the first time after installing the injectors I hooked up a new fuel pressure gauge I got from Summit. I turned the key and let the fuel system prime.

I noticed the fuel pressure jump to about 47-50PSI and drop off down to zero in around a minute. I removed the fuel pressure diaphragm and compressed the spring in my hand. I have a spare diaphragm and the spring on that one felt noticeably tighter so I installed it.

Repeating the fuel pressure test, the gauge jumps up to 50psi as before when the fuel system primes, but this time it holds it for several minutes before bleeding down. I figured this looked much better. I reassemble the remainder of the engine and start it up...

With the vacuum line connected on the fuel pressure regulator the gauge shows about 43.5PSI which is good. The I stop the engine, remove the vacuum line to the regulator, plug the vacuum ports and start the engine. The fuel pressure shows 50PSI.

As before the injectors were changed, the engine smells rich when in closed loop and a data log shows a rich BLM of 111. While it will rev it's not entirely happy about it.

So as I say, things are the same as before. Do you think I have eliminated fuel as the problem or might I have a problem with something else, like spark?

blackbeauty

After a bit more playing around, things are actually better than they were.

Presumably because the fuel pressure is no longer dropping off like it used to, I can start the engine and run it for a bit, shut it off, and start it up again straight away and it will start normally. I did this half a dozen times or so and each time the engine starts and keeps running.

I can also turn the key, let the fuel lines prime, wait a few minutes and then start the engine normally.

As you will have read earlier in this thread, this never worked right.

While the engine is running it idles at 43.5PSI. I rev it up and the fuel pressure increases to what appears to be a maximum of around 50PSI.

Can anyone tell me if the circumstances and numbers I've been quoting for fuel pressure are normal? If so then that particular issue is probably solved.

Assuming that's true, any pointers as to why it may be running rich? Bad leads, coil, ICM, plugs?

blackbeauty

Hi everyone,

I know it's been a while but this is a problem I'm still stuck with, I sure would appreciate some thoughts on this...

Thanks

ploegi

Fuel pressure is behaving correctly.

What size injectors did you get? Is the temp sensor reading correctly? TPS?

blackbeauty

Great, thanks for the confirmation on the fuel pressure.

I replaced the injectors with 19lb units from SouthBay, same flow rate as the Multechs I removed. Temp sensor and TPS are both giving me correct values.

Those two items even if incorrect wouldn't cause the engine to knock though would it?

91 zeee

I agree that your fuel pressures are now normal. Have you checked the timing ?

Tuned Performance

iTrader: (92)

blackbeauty

I did check the timing a while back and it appeared to retarded a couple of degrees so I set it back to 6 degrees BTDC. I recently checked it again and it appeared to be -4 degrees! Could be that I didn't tighten the distributor bolt enough although I thought I did.

Car does seem smelly rich. My clothes smell of it too.

When I give it gentle revs I can sense the car body shaking, I guess from the knocking. Unless it's my imagination, the body shudder seems worse when data logging. I know that on a stock tune (which this is), data logging adds 8 degrees to the timing.

As a simple test I swapped around the ESC module from a working '89 Trans Am into this one I'm trying to fix and I couldn't notice any difference.

I also disconnected the knock sensor and no noticeable difference. It might be better to disable the knock sensor by putting in a 3.9k resistor inline and see what happens.

Any other thoughts on things to check?

blackbeauty

Hey everyone,

Just to update on my situation. I measured the resistance of all the spark plugs wires and found one that was open circuit. I installed a new set and now the engine purrs like a kitten.

At least when the ECU is in open loop mode. As soon as it enters closed loop mode (engine already warm or not), it runs like crap and eventually stalls. But for that problem I'll search elsewhere on this board and make an appropriate posting if I need to.

Thanks to everyone to helped me get this far.

ploegi

If it runs like crap in closed loop, I would have a long hard look at the O2 sensor. If it is original, replace it.

blackbeauty

Oh you are good! I took the O2 sensor out and it was carbon black. Probably related to how come the plugs got black. I replaced the O2 sensor and that problem simply disappeared. Thank you very much!

Now I seem to have a intermittent code 34 occurring. I did see this happen once or twice before replacing the O2 sensor but figured it was a symptom rather than a cause. I'm going to swap the MAF and ECM from a working vehicle and see what difference that may make, and also the MAF relays.

Thanks again.

blackbeauty

Solved it. The final piece in the puzzle was...

The MAF sensor. I connected my digital volt meter betweens pins B and C on the MAF sensor with the engine running and it was clear it was faulty. I measured a constant 0.049 volts between these pins instead of the 700mV I should have got.

I plugged in a MAF sensor from another car and everything ran perfectly.

Case closed. Thanks everyone for your input.